Airfoil with cooling hole having a flared section

ABSTRACT

An airfoil is provided for a gas turbine engine. The airfoil may comprise a main body comprising a leading edge having a leading edge outer surface, a trailing edge having a trailing edge outer surface, a suction side having a suction side outer surface and a pressure side having a pressure side outer surface. The main body may further comprise at least one interior cooling passage and a plurality of cooling holes extending from the cooling passage to at least one of the leading edge outer surface, the trailing edge outer surface, the suction side outer surface and the pressure side outer surface. Preferably, at least one of the cooling holes includes a proximal metering section having a first dimension extending transverse to an axis extending in a flow direction of a cooling fluid passing through the one cooling hole, a flared section and an exit opening having a second dimension transverse to the axis which is larger than the first dimension. The flared section is preferably curvilinear as it extends from the proximal metering section towards the exit opening.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application Ser. No. 60/973,573, which was filed on Sep. 19, 2007, the disclosure of which is incorporated by reference in its entirety herein.

FIELD OF THE INVENTION

The present invention relates to an airfoil for a gas turbine engine having at least one cooling hole extending from an interior cooling passage to an outer surface of the airfoil and wherein the cooling hole has a flared section.

BACKGROUND OF THE INVENTION

A conventional combustion gas turbine engine includes a compressor, a combustor, and a turbine. The compressor compresses ambient air. The combustor combines the compressed air with a fuel and ignites the mixture creating combustion products defining a working gas. The working gases travel to the turbine. Within the turbine are a series of rows of stationary vanes and rotating blades. Each pair of rows of vanes and blades is called a stage. Typically, there are four stages in a turbine. The rotating blades are coupled to a shaft and disc assembly. As the working gases expand through the turbine, the working gases cause the blades, and therefore the shaft and disc assembly, to rotate.

Combustors often operate at very high temperatures. Typical combustor configurations expose turbine vanes and blades to these high temperatures. As a result, turbine vanes and blades must be made of materials capable of withstanding such high temperatures. In addition, turbine vanes and blades often contain cooling systems for prolonging the life of the vanes and blades and reducing the likelihood of failure as a result of excessive temperatures.

Conventional turbine blades and vanes have many different designs of internal cooling systems. For example, a plurality of cooling holes may extend from an interior cooling passage to an outer surface of an airfoil of a turbine vane or blade. It is preferred that the wall of the vane or blade be as thin as possible. It is also preferred that the cooling openings be shaped and sized such that the cooling fluid moving through each cooling opening does not separate from a wall defining the cooling opening.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, an airfoil is provided for a gas turbine engine. The airfoil may comprise a main body comprising a leading edge having a leading edge outer surface, a trailing edge having a trailing edge outer surface, a suction side having a suction side outer surface and a pressure side having a pressure side outer surface. The main body may further comprise at least one interior cooling passage and a plurality of cooling holes extending from the cooling passage to at least one of the leading edge outer surface, the trailing edge outer surface, the suction side outer surface and the pressure side outer surface. Preferably, at least one of the cooling holes includes a proximal metering section having a first dimension extending transverse to an axis extending in a flow direction of a cooling fluid passing through the one cooling hole, a flared section and an exit opening having a second dimension transverse to the axis which is larger than the first dimension. The flared section is preferably curvilinear as it extends from the proximal metering section towards the exit opening.

The one cooling hole may further comprise a distal section extending from at least a portion of the flared section to at least a portion of the exit opening.

In accordance with a first embodiment of the present invention, the one cooling hole may further comprise a concave interface section located between the flared section and the distal section. In accordance with a second embodiment of the present invention, the flared section meets directly with the distal section.

The proximal metering section may have a diameter D and a length between about 1.0D and about 5.0D. The diameter D of the proximal metering section may be from about 0.5 mm to about 5.0 mm.

The one cooling hole may extend at an angle θ of from about 20 degrees to about 90 degrees to the one outer surface.

The one outer surface may have a thickness T and the one cooling hole may have an overall length L determined from the following equation:

length L=thickness T/Sin θ

The exit opening may be substantially square or substantially circular in shape as viewed along the axis of the one cooling hole. With the exit opening square or circular in shape, the shape of the flared section may be defined by the following equation:

$y = \frac{y_{1}}{4 \times \sqrt{1 + {\left\lbrack {\left( {y_{1}/y_{0}} \right)^{4} - 1} \right\rbrack \cdot \left\lbrack {1 - \frac{x}{1_{d}}} \right\rbrack}}}$

wherein:

-   -   y₁=an exit radius or dimension for a largest portion of the         flared section;

y₀=a radius of the proximal metering section;

I_(d)=a length of a longest portion of the flared section;

x=independent coordinate extending along the axis with an origin at a beginning point of the flared section; and

y=dependent coordinate perpendicular to the axis with an origin at a central axis of the one cooling hole.

Alternatively, the shape of the flared section may be defined by the following equation:

$y = \frac{y_{1}}{\sqrt{1 + {\left\lbrack {\left( {y_{1}/y_{0}} \right)^{2} - 1} \right\rbrack \cdot \left\lbrack {1 - \frac{x}{1_{d}}} \right\rbrack}}}$

wherein:

-   -   y₁=an exit radius or dimension for a largest portion of a         curvilinear portion of the flared section;     -   y₀=a radius of the proximal metering section;     -   I_(d)=a length of a longest portion of the flared section;     -   x=independent coordinate extending along the axis with an origin         at a beginning of the flared section; and     -   y=dependent coordinate perpendicular to the axis with an origin         at a center axis of the one cooling hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 2A illustrate a cooling hole constructed in accordance with a first embodiment of the present invention;

FIG. 3 is a perspective view, partially in cross section, of a blade in which the cooling holes of the present invention may be incorporated;

FIGS. 4, 5 and 5A illustrate a cooling hole constructed in accordance with a second embodiment of the present invention;

FIG. 6 is an enlarged view of the circled portion labeled 6 in FIG. 4 with a concave section of an alternative embodiment illustrated in dotted line;

FIG. 7 is an enlarged view of the circled portion labeled 7 in FIG. 5 with a concave section of an alternative embodiment illustrated in dotted line; and

FIGS. 8, 9 and 9A illustrate a cooling hole constructed in accordance with a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 3, a blade 10 constructed in accordance with the present invention is illustrated. The blade 10 is adapted to be used in a gas turbine (not shown) of a gas turbine engine (not shown). Within the gas turbine are a series of rows of stationary vanes and rotating blades. Typically, there are four rows of blades in a gas turbine.

The blades are coupled to a shaft and disc assembly. Hot working gases from a combustor (not shown) in the gas turbine engine travel to the rows of blades. As the working gases expand through the turbine, the working gases cause the blades, and therefore the shaft and disc assembly, to rotate.

The blade 10 comprises an attachment portion or a root 12, a platform 14 integral with the root 12 and an airfoil 20 formed integral with the platform 14, see FIG. 3. The root 12 functions to couple the blade 10 to the shaft and disc assembly (not shown) in the gas turbine (not shown). The airfoil 20 is defined by a main body 100 comprising a tip (not shown), a root section or a base 110, a leading edge 120, a trailing edge 130, a concave-shaped pressure side 140, and a convex-shaped suction side 150. The airfoil leading edge 120 has a leading edge outer surface 122, the airfoil trailing edge 130 has a trailing edge outer surface 132, the airfoil pressure side 140 has a pressure side outer surface 142 and the airfoil suction side 150 has a suction side outer surface 152. The main body 100 may be formed as a single integral unit from a material such as a metal alloy 247 via a conventional casting operation.

A conventional thermal barrier coating (not shown) is provided on an outer surface 102 of the main body 100. The outer surface 102 of the main body 100 is defined by the leading edge outer surface 122, the trailing edge outer surface 132, the pressure side outer surface 142 and the suction side outer surface 152.

In the illustrated embodiment, the airfoil main body 100 further comprises an interior cooling passage 160 and a plurality of cooling holes 170 extending from the cooling passage 160 to at least one of the leading edge outer surface 122, the trailing edge outer surface 132, the pressure side outer surface 142 and the suction side outer surface 152, see FIG. 3. While only a single interior cooling passage 160 is illustrated in the FIG. 3 embodiment, two or more interior cooling passages may be provided in the airfoil main body 100. Also, while only three cooling holes 170 are illustrated in the pressure side 140 of the embodiment of FIG. 3, one, two or four or more cooling holes 170 may be provided in the pressure side 140 and one or more cooling holes 170 may be provided in the leading edge 120, the trailing edge 130, and/or the convex-shaped suction side 150.

A cooling fluid, such as air or steam, is supplied under pressure in the direction of arrow A in FIG. 3 to a cooling fluid entrance (not shown) provided in the root 12. The cooling fluid may be supplied by the compressor (not shown) of the gas turbine engine via conventional supply structure (not shown) extending to the cooling fluid entrance channel.

The cooling fluid moves through the cooling fluid entrance, through the platform 14 and into the interior cooling passage 160 of the airfoil main body 100. From the airfoil cooling passage 160, the cooling fluid passes through the cooling holes 170 and, after exiting the cooling holes 170, provides film cooling for a downstream portion, i.e., in a direction away from the leading edge 120 toward the trailing edge 130, of the outer surface 102 of the main body 100.

Each of the cooling holes 170 may be formed so as to have substantially the same shape and size. Hence, only a single cooling hole, for each embodiment of cooling holes, will be discussed herein.

Referring now to FIGS. 1 and 2, a cooling hole 170 formed in accordance with a first embodiment of the present invention may extend to the outer surface 102 of the main body 100 at an angle θ of from about 20 degrees to about 90 degrees. The cooling hole 170 may comprise a proximal metering section 172 having a diameter D₁₇₂ extending transverse to a central axis A₁₇₀ of the cooling hole 170, wherein the central axis A₁₇₀ extends in a flow direction FD of a cooling fluid passing through the cooling hole 170. The diameter D₁₇₂ of the proximal metering section 172 may be from about 0.5 mm to about 5.0 mm. An entrance 172A of the proximal metering section 172 defines an entrance for the cooling hole 170 and communicates with the interior cooling passage 160. The cooling hole 170 further comprises a flared section 174 connected with and extending away from the proximal metering section 172; a distal section 176 connected with and extending away from a portion of the flared section 174; and an exit opening 178 connected to the distal section 176 and a portion of the flared section 174.

In the embodiment illustrated in FIGS. 1 and 2, the flared section 174 has a curvilinear shape as it extends away from the proximal metering section 172 towards the distal section 176 and the exit opening 178 in an X direction, see FIGS. 2 and 2A. In a Y-Z plane, the flared section 174 has a generally circular shape. Because the cooling hole 170 is positioned at an angle θ less than 90 degrees relative to the outer surface 102 of the main body 100, a length of a first portion 174A of the flared section 174 in the X direction is greater than a length of a second portion 174B of the flared section 174, see FIG. 2. If the second portion 174B had a length equal to the length of the first portion 174A, it would have an additional section 174C, shown in dotted line in FIG. 2. The shape of the flared section 174 may be defined by the following equation:

$\begin{matrix} {y = \frac{y_{1}}{4 \times \sqrt{1 + {\left\lbrack {\left( {y_{1}/y_{0}} \right)^{4} - 1} \right\rbrack \cdot \left\lbrack {1 - \frac{x}{1_{d}}} \right\rbrack}}}} & \left( {{Equation}\mspace{14mu} 1} \right) \end{matrix}$

wherein:

-   -   y₁=an exit radius for the largest portion, i.e., the first         portion 174A, of the flared section 174;     -   y₀=a radius of the proximal metering section 172;     -   I_(d)=a length of the longest portion, i.e., the first portion         174A, of the flared section 174;     -   x=independent coordinate extending along the central axis A₁₇₀         of the cooling hole 170 with an origin at a beginning point         P_(B174) of the flared section 174; and     -   y=dependent coordinate perpendicular to the central axis A₁₇₀ of         the cooling hole 170 with an origin at the central axis A₁₇₀.

The radius y₀ (also referred to herein as “a first dimension”) of the proximal metering section 172 is less than a largest dimension (also referred to herein as “a second dimension”) of the exit opening 178.

The shape and size of the cooling hole 170 may be designed as follows. Typically, the thickness T of the airfoil main body 100 is predefined. Also, the diameter D₁₇₂ of the proximal metering section 172 is predefined and typically selected to be as small as possible, e.g., 1 mm, so as to minimize the risk that the cooling hole 170 may be blocked by dirt and the like. With the diameter D₁₇₂ of the proximal metering section 172 equal to about 1 mm, the main body thickness T may equal 3.8D₁₇₂ or 3.8 mm. The angle θ, the angle at which the cooling hole 170 is positioned relative to the outer surface 102 of the main body 100, is also predefined and is typically selected to be as small as possible so as to be within manufacturing capabilities.

With the angle θ and the thickness T of the airfoil main body 100 predefined, the overall length L₁₇₀ of the cooling hole 170 may be determined via the following equation:

length L ₁₇₀=thickness T/Sin θ  (Equation 2)

With the angle θ and the thickness T of the airfoil main body 100 predefined and the overall length L₁₇₀ of the cooling hole 170 predetermined, different values of y₁/y₀ and I_(d) from Equation 1, above, are selected and tested to determine the values for y₁/y₀ and I_(d) which provide a desired film cooling effectiveness for the outer surface 102 of the airfoil main body 100. The length L₁₇₂ of the proximal metering section 172 is equal to the overall length L₁₇₀ of the cooling hole 170 minus the length I_(d) of the longest portion, i.e., the first portion 174A, of the flared section 174. Equation 1, above, is then used to determine values for x and y, i.e., the shape, of the flared section 174.

In prior art cooling holes, a transition section extending away from the proximal metering section towards an exit opening had a straight or linear shape as the transition section expanded away from the metering section. If the metering section had a length less than about 5.0D (where D=the diameter of the metering section), there was risk that the cooling fluid would separate from the wall defining the transition section, causing a reduction in film cooling for a downstream portion of the outer surface of the airfoil main body. Because the flared section 174 of the cooling hole 170 of the present invention has a curvilinear shape as it extends away from the proximal metering section 172 towards the distal section 176 and exit opening 178 in a X direction, see FIGS. 2 and 2A, it is believed that a cooling fluid moving from the proximal metering section 172, through the flared section 174 and into the distal section 176 or exit opening 178 will have an increased likelihood of not separating from a wall W₁₇₄ defining the flared section 174, even if the metering section 172 has a length L₁₇₂ less than about 5.0D₁₇₂.

In the embodiment illustrated in FIGS. 1 and 2, the flared section 174 meets directly with the distal section 176 or the exit opening 178. However, it is also contemplated that a concave interface section (not shown) may be provided between the flared section 174 and the distal section 176.

In FIGS. 4 and 5, a cooling hole 270 formed in accordance with a second embodiment of the present invention, where like elements are referenced by like reference numerals, is illustrated. The cooling hole 270 may extend to the outer surface 102 of the main body 100 at an angle θ of from about 20 degrees to about 90 degrees. The cooling hole 270 may comprise a proximal metering section 272 having a diameter D₂₇₂ extending transverse to a central axis A₂₇₀ of the cooling hole 270, wherein the central axis A₂₇₀ extends in a flow direction FD of a cooling fluid passing through the cooling hole 270. The diameter D₂₇₂ of the proximal metering section 272 may be from about 0.5 mm to about 5.0 mm. An entrance 272A of the proximal metering section 272 defines an entrance for the cooling hole 270 and communicates with the interior cooling passage 160. The cooling hole 270 further comprises a flared section 274 connected with and extending away from the proximal metering section 272; a distal section 276 connected with and extending away from a portion of the flared section 274; and an exit opening 278 connected to the distal section 276 and a portion of the flared section 274.

In the embodiment illustrated in FIGS. 4 and 5, the flared section 274 has a curvilinear shape as it extends away from the proximal metering section 272 towards the distal section 276 and exit opening 278 in an X direction, see FIGS. 5 and 5A. In a Y-Z plane, the flared section 274 has a generally square shape. Because the cooling hole 270 is positioned at an angle θ less than 90 degrees relative to the outer surface 102 of the main body 100, a length of a first portion 274A of the flared section 274 in the X direction is greater than a length of a second portion 274B of the flared section 274, see FIG. 5. If the second portion 274B had a length equal to the length of the first portion 274A, it would have an additional section 274C, shown in dotted line in FIG. 5. The shape of the flared section 274 may be defined by Equation 1 above, wherein:

y₁=an exit radius or dimension for the largest portion, i.e., the first portion 274A, of the flared section 274;

y₀=a radius of the proximal metering section 272;

I_(d)=a length of the longest portion, i.e., the first portion 274A, of the flared section 274;

x=independent coordinate extending along the central axis A₂₇₀ Of the cooling hole 270 with an origin at a beginning point P_(B274) of the flared section 274; and

y=dependent coordinate perpendicular to the central axis A₂₇₀ of the cooling hole 270 with an origin at the central axis A₂₇₀. In this embodiment, values for z substantially equal values for y, when both z and y have the same corresponding x value.

The shape and size of the cooling hole 270 may be designed using generally the same steps set out above for designing the cooling hole 170 of the first embodiment.

In the embodiment illustrated in FIGS. 4 and 5, the flared section 274 meets directly with the distal section 276. However, it is also contemplated that a concave interface section 275 may be provided between the flared section 274 and the distal section 276, see FIGS. 6 and 7 wherein the concave section 275 is shown in dotted line.

In FIGS. 8 and 9, a cooling hole 370 formed in accordance with a third embodiment of the present invention, where like elements are referenced by like reference numerals, is illustrated. The cooling hole 370 may extend to the outer surface 102 of the main body 100 at an angle θ of from about 20 degrees to about 90 degrees. The cooling hole 370 may comprise a proximal metering section 372 having a diameter D₃₇₂ extending transverse to a central axis A₃₇₀ of the cooling hole 370, wherein the central axis A₃₇₀ extends in a flow direction FD of a cooling fluid passing through the cooling hole 370. The diameter D₃₇₂ of the proximal metering section 372 may be from about 0.5 mm to about 5.0 mm. An entrance 372A of the proximal metering section 372 defines an entrance for the cooling hole 370 and communicates with the interior cooling passage 160. The cooling hole 370 further comprises a flared section 374 connected with and extending away from the proximal metering section 372; a distal section 376 connected with and extending away from a portion of the flared section 374; and an exit opening 378 connected to the distal section 376 and a portion of the flared section 374.

In the embodiment illustrated in FIGS. 8 and 9, the flared section 374 has a curvilinear shape in a Y direction as it extends away from the proximal metering section 372 and towards the distal section 376 and first sides 378A of the exit opening 378 in an X direction, see FIGS. 9 and 9A. It is noted that the Y and Z axes have been reversed in this embodiment from their respective positions in the embodiments of FIGS. 2, 2A, 5 and 5A. The flared section 374 has at least one planar wall 374A spaced away from the central axis A₃₇₀ by a distance equal to diameter D₃₇₂/2 or y₀. The shape of the flared section 374 in the Y direction may be defined by Equation 3:

$y = \frac{y_{1}}{\sqrt{1 + {\left\lbrack {\left( {y_{1}/y_{0}} \right)^{2} - 1} \right\rbrack \cdot \left\lbrack {1 - \frac{x}{1_{d}}} \right\rbrack}}}$

wherein:

-   -   y₁=an exit radius or dimension for a largest portion of a         curvilinear portion of the flared section 374;     -   y₀=a radius of the proximal metering section 372;     -   I_(d)=a length of the longest portion of the flared section 374;     -   x=independent coordinate extending along the central axis A₃₇₀         of the cooling hole 370 with an origin at a beginning point         P_(B374) of the flared section 374; and     -   y=dependent coordinate perpendicular to the central axis A₃₇₀ of         the cooling hole 370 with an origin at the central axis A₃₇₀.

The shape and size of the cooling hole 370 may be designed using generally the same steps set out above for designing the cooling hole 170 of the first embodiment.

While a particular embodiment of the present invention has been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

1. An airfoil for a gas turbine engine comprising: a main body comprising a leading edge having a leading edge outer surface, a trailing edge having a trailing edge outer surface, a suction side having a suction side outer surface and a pressure side having a pressure side outer surface, said main body further comprising at least one interior cooling passage and a plurality of cooling holes extending from said cooling passage to at least one of said leading edge outer surface, said trailing edge outer surface, said suction side outer surface and said pressure side outer surface; at least one of said cooling holes including a proximal metering section having a first dimension extending transverse to an axis extending in a flow direction of a cooling fluid passing through said one cooling hole, a flared section and an exit opening having a second dimension transverse to the axis which is larger than said first dimension, wherein said flared section is curvilinear as it extends from said proximal metering section towards said exit opening.
 2. An airfoil as set out in claim 1, wherein said one cooling hole further comprises a distal section extending from at least a portion of said flared section to at least a portion of said exit opening.
 3. An airfoil as set out in claim 2, wherein said one cooling hole further comprises a concave interface section located between said flared section and said distal section.
 4. An airfoil as set out in claim 2, wherein said flared section meets directly with said distal section.
 5. An airfoil as set out in claim 1, wherein said proximal metering section has a diameter D and a length between about 1.0D and about 5.0D.
 6. An airfoil as set out in claim 5, wherein said one cooling hole extends at an angle θ of from about 20 degrees to about 90 degrees to said one outer surface.
 7. An airfoil as set out in claim 6, wherein said one outer surface has a thickness T and said one cooling hole has an overall length L determined from the following equation: length L=thickness T/Sin θ
 8. An airfoil as set out in claim 5, wherein said diameter D of said proximal metering section is from about 0.5 mm to about 5.0 mm.
 9. An airfoil as set out in claim 1, wherein the shape of said flared section is defined by the following equation: $y = \frac{y_{1}}{4 \times \sqrt{1 + {\left\lbrack {\left( {y_{1}/y_{0}} \right)^{4} - 1} \right\rbrack \cdot \left\lbrack {1 - \frac{x}{1_{d}}} \right\rbrack}}}$ wherein: y₁=an exit radius or dimension for a largest portion of said flared section; y₀=a radius of said proximal metering section; I_(d)=a length of a longest portion of said flared section; x=independent coordinate extending along the axis with an origin at a beginning of said flared section; and y=dependent coordinate perpendicular to the axis with an origin at a central axis of said one cooling hole.
 10. An airfoil as set out in claim 9, wherein said exit opening is square or circular in shape as viewed along the axis of said one cooling hole.
 11. An airfoil as set out in claim 1, wherein the shape of said flared section is defined by the following equation: $y = \frac{y_{1}}{\sqrt{1 + {\left\lbrack {\left( {y_{1}/y_{0}} \right)^{2} - 1} \right\rbrack \cdot \left\lbrack {1 - \frac{x}{1_{d}}} \right\rbrack}}}$ wherein: y₁=an exit radius or dimension for a curvilinear portion of said flared section; y₀=a radius of said proximal metering section; I_(d)=a length of a longest portion of said flared section; x=independent coordinate extending along the axis with an origin at a beginning of said flared section; and y=dependent coordinate perpendicular to the axis with an origin at a central axis of said one cooling hole. 